Accidentally? Hello? I don't think so. I have friends who know their mom passwords and they use it to take money from their accounts and make purchases online and I mean expensive purchases!
I make sure my children do not have access to my money and are not able to make a online purchase. Feel that if they need to buy something on line they can go out and get their own job and then they can buy what ever they want on line or in a real store. I would say those that give their children access to their accounts are not helping their kids learn about money and spending.
Accidentally? Ha! If the child took your credit card and spent your money on an Massive Multi-player Online Role-playing Game, then it is not 'accidental spending'--it is theft. Punish your child for his crime and make him do chores to earn back what he stole. Be sure to lock your credit card in a safe so this does not happen again.